#include<bits/stdc++.h>
using namespace std;
int a(int n){
  float r;
  if(n==1) r=1;
  if(n==2) r=2;
  if(n>2) r=a(n-2)+a(n-1);
  return r;
  } 
int main(){
  int n,i;
  float s=1;
  cin>>n;
  for(i=1;i<n;i++) s=s+a(i)*1.000/a(i+1);
  printf("%.3f",s);
  return 0;
}
/**************************************************************
	Problem: 1147
	User: wtq001
	Language: C++
	Result: Accepted
	Time:8 ms
	Memory:2072 kb
****************************************************************/